The present invention relates to a control device for an at least partially four-wheel-driven motor vehicle. More particularly, the present invention relates to a control device for an at least partially four-wheel-driven motor vehicle, having a control unit which variably distributes driving torque of a drive unit to primary driving wheels, which are permanently connected with the drive unit, and to secondary driving wheels which, if required, can be connected by way of a transfer clutch with the drive unit, wherein the control unit determines a desired clutch torque which is to be set by means of an actuator device at the transfer clutch.
A control device of this type is described, for example, in German Patent Document DE 100 54 023 A1. Accordingly, a torque distribution device is known for changing the torque distribution ratio between the wheels of the front axle and the wheels of the rear axle by a corresponding control of a friction clutch as a longitudinal blocking device (i.e., transfer clutch). The driving action of a vehicle can be influenced considerably by the determination of a torque distribution ratio. In particular, the object of German Patent Document DE 100 54 023 A1 relates to the driving dynamics when cornering. In this case, a partially four-wheel-driven motor vehicle may be a basically front-wheel-driven motor vehicle with a rear-wheel drive which can be connected by means of a transfer clutch; a basically rear-wheel-driven motor vehicle with a front-wheel drive which can be connected by way of a transfer clutch; or a permanent all-wheel drive vehicle with a controllable transfer clutch for changing the torque distribution between the front and rear axle.
In general, as described below, primary driving wheels are the wheels which are permanently connected with the drive unit, and secondary driving wheels are the wheels which, if required, can be connected with the drive unit by way of the transfer clutch.
Furthermore, such known control systems usually have a control of the transfer clutch as a function of the rotational speed difference between a rotational speed of the primary driving axle and the rotational speed of the secondary driving axle (for example, German Patent Document DE 34 27725 C2).
It is an object of the present invention to improve a control system of the initially mentioned type with respect to the availability of the transfer clutch and/or of the actuator device for controlling the transfer clutch.
The present invention is based on the recognition that, among other things, partly contradictory demands are the result of trying to achieve an increase of the availability of the transfer clutch and/or of the actuator device when determining the desired clutch torque. These different demands are first reflected inside the control unit by different intermediate desired clutch torques which have to be coordinated in order to obtain a final desired clutch torque which actually is to be set. An object of the present invention is, therefore, particularly a torque coordination in the form of a prioritization structure of different intermediate desired clutch torques which also take into account demands with respect to driving dynamics.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.